• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1997년도 추계학술대회 논문집
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• pp.13-20
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• 1997

In this paper, the voltage step-up ratio, efficiency and input impedance of the PMN-PZT cert- mic transformer(PT) were investigated for the variation of resonant frequency according to lead resistance. The output voltage and voltage step-up ratio are increased with the the increase of load resistance. The efficiency of PT showed the maxinum value of 91% at R$_{L}$ of 500k$\Omega$X>

• 한국산림과학회지
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• 제100권2호
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• pp.202-211
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• 2011

강원도 춘천시 근교의 강원대학교 산림환경과학대학 학술림 내의 산지계류를 대상으로 계단상 하상구조의 기하학적 특성과 이에 대한 계류 지형인자들과의 관계를 분석하였다. 조사구간에 형성된 스텝의 간격, 높이 및 낙차의 평균값은 각각 4.69 m, 0.47 m 및 0.71 m, 스텝의 구성입경은 평균 0.68 m, 스텝의 형성개수는 100 m당 평균 21 개인 것으로 나타났다. 스텝의 간격은 하폭대비 약 0.5로 선행연구들에 비해 작은 것으로 나타났으며, 스텝의 기울기는 평균 0.13이었다. 스텝의 각 기하학적 특성과 하폭과의 사이에는 모두 상관관계가 존재하지 않았으나, 스텝의 간격과 높이는 하상경사와 각각 부 정의 상관관계를 나타내었다. 또한 스텝의 기울기는 하상경사와 정의 상관을 보였고, 하상경사와의 비가 1.2로 나타나 유수에 대한 최대저항조건을 만족하며 비교적 안정상태를 유지하고 있는 것으로 나타났다. 특히 하상경사는 계단상 하상구조의 기하학적 형상(스텝의 낙차와 높이의 비)에 영향을 미치는 것으로 나타났다. 한편 스텝의 간격과 낙차는 거석의 입경과 모두 정의 상관관계를 보였다. 이러한 결과들로부터 계단상 하상구조의 동태는 산지계류의 물리 생태적 환경에 큰 영향을 미칠 것으로 판단되며, 산지가 대부분인 우리나라의 계류관리에 있어서 특히 중요하게 인식되어야 할 것이다.

• 대한물리의학회지
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• 제8권3호
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• pp.397-406
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• 2013

PURPOSE: The Purpose of this study was on determine whether stair gait exercise and lamp gait exercise might increase the gait ability of the patients with stroke METHODS: Fourty five patients with stroke were randomly assigned to plane gait exercise group(n=15) and ramp gait exercise group(n=15) and stair gait exercise group(n=15). During four weeks, each group participated thirty minutes for five times per week. Subjects were assessed using pre-value and post-value measurement gait ability(Step length, Heel to heel base of support, Step time, Double support ratio, Gait velocity). RESULTS: These finding suggest that stair gait exercise group was significant in Step length, Heel to heel base of support, Step time, Double support ratio, Gait velocity(p<.05). And lamp gait exercise group was only significant increase in Step time, Gait velocity(p<.05). In comparison of three group, stair gait exercise group was high gait ability than other two groups(p>.05). CONCLUSION: This study showed stair gait exercise group can be used to improve gait ability than other two groups. Thus it indicates that the stair gait exercise group will be more improved through the continued gait program.

• 국토계획
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• 제54권1호
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• pp.40-51
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• 2019

The ultimate aim of this study is to diagnose the process stage and look at the step change of transition process to see how the step changes. Therefore, in this study, cluster analysis was conducted by examining four types of commercial characteristics such as Retail Homogeneity, Share of Neighbourhood store, Share of chain store, and Share of cafe & Western food store. Through the cluster analysis, three types have been identified. Type1 is the first step which can explain the time before gentrification occurs and when the ratio of neighborhood facilities is the highest. Type2 is the second step that can explain boutique stage where the gentrification occurs. At this time, the ratio of Cafes & Western food restaurant increased and the proportion of neighborhood shops decreased. And Type3, third step is when the mature gentrification occurs. In the analysis of the transition period, it is necessary to monitor the change of the industry in the period from the first stage to the second stage. In the transition period from the second stage to the third stage, It is necessary to constantly monitor such factors as the increase of shops.

• 한국자동차공학회논문집
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• 제14권1호
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• pp.92-99
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• 2006

The swirl ratio of a charge in the cylinder was estimated by calculating the ratio of the rotary speed of charge which could be simulated from the rotary speed of paddle in the swirl measurement apparatus, to the engine speed which could be calculated by measuring intake air flow rate. The automation of the swirl ratio measurement for cylinder head was achieved by controling both valve lift in cylinder head and a suction pressure of surge tank using two step-motors. The number of measurement position for calculating mean swirl ratio was varied by adjusting the interval of valve lift. The mean swirl ratio with varying the number of measurement position showed nearly constant value. Two measurement methods for measuring the swirl ratio were compared, one was to control the suction pressure of the surge tank with PID (proportional, integral, differential) mode with by-pass valve controlled by the step motor and the other did not control the surge tank pressure by fixing the by-pass valve. The difference of the mean swirl ratio between the two measurement methods showed nearly constant value with varying the number of measurement position. This means that the w/o PID control method could be preferred to the PID control method which has been used, due to the simpleness of the swirl measurement.

• 한국수자원학회논문집
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• 제31권3호
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• pp.243-252
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• 1998

본 연구에서는 새로운 무차원값을 제시하여 도시유출모형의 매개변수결정을 위한 상대적인 민감도분석을 실시하여 매개변수별 민감도특성을 구명하였다. 민감도분석을 위한 무차원값으로 총유출량비,첨두유출량비, 유출민감도비, 민감도비율을 다음과 같이 개발하였다. $$ 유역면적의 크기와 강우분포형과 강우지속기간별로 각 적용단계별 총유출량비, 첨두유출량비, 유출민감도를 산정하기 위해 ILLUDAS모형과 SWMM모형의 매개변수를 선저하고 적정 적용범위를 결정하였다.

• Structural Engineering and Mechanics
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• 제39권5호
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• pp.683-701
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• 2011

In this study, inelastic displacement ratios and ductility demands are investigated for SDOF systems with period range of 0.1-3.0 s. with elastoplastic behavior considering soil structure interaction. Earthquake motions recorded on different site conditions such as rock, stiff soil, soft soil and very soft soil are used in analyses. Soil structure interacting systems are modeled with effective period, effective damping and effective ductility values differing from fixed-base case. For inelastic time history analyses, Newmark method for step by step time integration was adapted in an in-house computer program. Results are compared with those calculated for fixed-base case. A new equation is proposed for inelastic displacement ratio of interacting system ($\tilde{C}_R$) as a function of structural period of interacting system ($\tilde{T}$), strength reduction factor (R) and period lengthening ratio ($\tilde{T}/T$). The proposed equation for $\tilde{C}_R$ which takes the soil-structure interaction into account should be useful in estimating the inelastic deformation of existing structures with known lateral strength.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 C
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• pp.1490-1492
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• 2003

A new type of piezoelectric transformer using radial vibration of disk, poled with the same direction is proposed. The piezoelectric ceramics was composed to PZT-PMN-PSN. The surface ratio of driving electrode and generating electrode of the piezoelectric transformer ranges from 1.4:1 to 3:1. As a experimental result, both resonance frequency and step-up voltage ratio increased with increasing load resistance. The step-up voltage ratio was reached more than 60 times under no load resistance. The maximum efficiency of 97.7% at load resistance of 2k${\Omega}$ was obtained.

• 전력전자학회논문지
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• 제19권4호
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• pp.349-356
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• 2014

As the turns ratio of the tapped-inductor contributes to the step-up ratio, the tapped-inductor boost (TIB) converter has significantly increased level of difficulties in its analysis and design compared to the conventional boost converter where the duty ratio is the sole factor affecting the step-up ratio. In this paper, the operation of the continuous current mode TIB converter is briefly reviewed, the characteristics are analyzed in detail, and a design guideline optimizing the loss in the tapped-inductor is presented with a practical design example. Finally, experimental results from a 12V/120V prototype for 0.25A LED driver application are also presented to confirm the design.

• 한국결정성장학회지
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• 제26권3호
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• pp.89-94
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• 2016

본 연구에서는 HVPE(Hydride Vapor Phase Epitaxy)를 이용하여 각각 다른 V/III ratio를 가지는 multi-step의 성장 시간 변화에 따라 r-plane 사파이어 위에 성장되는 a-plane GaN 에피층의 결정성에 대하여 연구하였다. 또한 이번 연구의 결과를 선행 연구에서 single-step으로 r-plane 사파이어 위에 성장시킨 a-GaN 에피층의 결과와 비교하였다. Multi-step으로 r-plane 사파이어 위에 a-plane GaN 에피층을 성장시켰을 때, source HCl의 유량과 성장 시간이 증가함에 따라 a-plane GaN 에피층에 대한 rocking curve의 FWHM(Full Width at Half Maximum) 값이 감소하였다. 높은 source HCl의 유량을 갖는 first step과 second step의 성장 시간과 source HCl의 유량이 증가할수록 a-plane GaN 에피층 내부의 void가 감소하였다. 결과적으로 first step과 second step의 성장 시간이 가장 긴 조건에서 성장된 a-plane GaN 에피층이 가장 낮은 FWHM 값인 584 arcsec을 가지며, azimuth angle의 의존도가 가장 적은 것으로 확인되었다.